Centrifugally variable diffuser for marine propeller



United States Patent Inventors Carl Knuth Fond Du Lac, Wisconsin;

Appl. No. 856,000 Filed Sept. 8, 1969 Patented Nov. 24, 1970 Assignee Brunswick Corporation Chicago, Illinois a corporation of Delaware CENTRIFUGALLY VARIABLE DIFFUSER FOR MARINE PROPELLER 7 Claims, 4 Drawing Figs.

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Int. Cl

Primary ExaminerEverette A. Powell, Jr. AttorneyRoy T. Montgomery ABSTRACT: A centrifugally variable diffuser portion is disclosed for a marine propulsion propeller of the type adapted to receive and conduct engine exhaust products through the hub for discharge rearwardly thereof through the exhaust discharge opening defined by the diffuser portion.

Patented 7 Nov. 24, 1970 3,542,487

PNVENTOR. CARL KNUTH Attorneys CENTRIFUGALLY VARIABLE DIFFUSER FOR MARINE PROPELLER This invention relates to a propeller for a marine propulsion unit and more particularly to apropeller adapted to receive and conduct engine exhaust gases through the hub thereof for discharge rearwardly ofthe propeller. i

In a through the propeller hub exhaust system the water flowing over the hub tends to converge relatively quickly aft of the propeller exhaust discharge opening. The rapid convergence of water aft of the propeller may interfere with the free flow of exhaust products from the engine driving the unit and so gives rise to possible back pressures in the exhaust system to adversely affect engine efficiency. US, Pat. No. 2,948,252, assigned to the common assignee with this invention, discloses an effective manner for treating with the problem and suggests that the periphery of the propeller hub immediately adjacent to the exhaust discharge opening be provided with a given fixed water converging retarding surface. It is generally an object of this invention to provide a variable water converging retarding surface aft of the propeller hub to better suit the varying drive conditions of the propulsion unit,

According to the invention, a marine propeller which is adapted to receive and conduct engine exhaust products through the hub thereof for discharge rearwardly of the propeller includes a cylindrical diffuser portion on the rearward end of the propeller hub'and which defines the exhaust discharge opening. The diffuser portion is radially expandable adjacent to the exhaust discharge opening in response to centrifugal force resulting from propeller rotation in operation to suit the varying drive conditions of the propulsion unit.

The drawings furnished herewith illustrate the best mode presently contemplated for carrying out the invention described hereinafter.

In the drawings: a

FIG, I is a side elevation of an outboard motor with parts broken away and sectioned and includes the propeller conthe diffuser portion as results from the interaction of the centrifugal force caused by the rotating propeller and the slipstream ram pressure caused by the travel of the propeller through the water;

FIG. 3 is an end elevation ofthe propeller with parts broken away and sectioned to better show the flyweight arrangement in the diffuser portion; and

FIG. 4 is a partial end elevation of the propeller and shows an embodiment having a spring flyweight arrangement in the diffuser portion.

Referring to the drawings, the invention is applied to an outboard propulsion unit such as the outboard motor 1 adapted for securement onto a watercraft,not shown, to propel such craft.

The outboard motor 1 comprises an engine 2 enclosed within the cowl 3 and supported on the drive shaft housing 4. A lower underwater unit 5 is carried at the lower end of the drive shaft housing 4 and rotatably supports a generally horizontal propeller shaft 6 which is drivingly connected to the engine 2. The propeller shaft 6 projects rearwardly from the lower unit 5 through the opening 7 and carries the propeller 8 for rotation therewith aft of the unit.

The exhaust products from the engine 2 are conducted downwardly through the housing 4 to the lower unit 5 by means of the passage means 9 which communicate with the opening 7. From the lower unit 5, the exhaust products pass through the opening 7 and are conducted through the annular passage I0 formed between the inner and outer hubs I1 and 12 respectively of the propeller 8 for discharge rearwardly of the propeller through the hub discharge opening 13.

According to this invention, the propeller 8 is provided aft with an annular, centrifugally variable diffuser portion 14 which is generally in the form of an extension on the outer hub 2 12. As generally shown" in FIG.. 2, the outer hub 12 of propeller 8 is stepped inwardly to provide an annular rearwardly extending flange 15 for attachment ofthe diffuser por- 1 tion 14. Diffuser portion 14 is stepped outwardly to provide a forwardly extending annular flange 16 to complement the flange 15 on hub 12. In the assembly of the diffuser portion 14 onto the propeller hub 12 the annular flange 15 overlays the complementary annular flange 16 with the ends of the respec tive flanges abutting the shoulders 17 and 18 on the diffuser portion and hub, respectively, such that the connection therebetween provides a generally smooth uninterrupted transition both internally and externally of the hubv The engaging surfaces between hub 12 and its diffuser portion 14 are secured by bonding and the securement may be enhanced by engagement of a peripheral locking bead 19 on the diffuser portion flange l6 withina complementary recess 20 interiorly of the hub flange 15.

The annular hub diffuser portion 14 is fabricated from rubber or other suitable resilient, expandable material. Adjacent to the hub discharge opening 13, the hub diffuser portion 14 is provided with an annular radial enlargement 21 which carries a plurality of circumferentially spaced balls 22 of lead shot or the like which serve as flyweights and may be molded into the diffuser portion. The tlyweight balls 22 provide a generally even distribution of weight cireumferentially so that the diffuser portion 14 will react centrifugally with rotation of the propeller 8, as will be further described hereinafter, to flare the diffuser portion: outwardly as generally shown in phantom lines in FIG. 2. The centrifugally formed flare on diffuser portion 14 provides the water flowing over the propeller hub with a radial outward component to thereby retard the convergence of the waters aft of the discharge opening 13 so that the exhaust flow atthe opening 13 is not restricted. Intermediate the enlargement 21 and the flange 16 the diffuser portion 14 may be provided with a region of reduced radial thickness as at 23 to enhance the expandability of the diffuser portion and provide the desired flare configu ration in service.

As the propeller 8 moves through the water in service, the water moving along the outside surface of the outer propeller hub 12 including the'diffuser portion 14 sets up a slipstream ram pressure which acts as a force generally paralleling the hub surface and which tends to counteract the flaring of the diffuserportion due to the centrifugal force resulting from propeller rotation. It is the interaction between the slipstream ram pressure andthe centrifugal force which determines the degree of flaring of the diffuser portion 14.

In operation and when the engine 2 is operating to rotate the propeller 8 at a low or moderate revolutions per minute, the outboard motor I and its watercraft will travel relatively slowly (as in trolling for example). At such speeds of the watercraft, the slipstream ram pressure will be so low as to have little, if any, effect on the flaring resulting from the centrifugal force due to propeller rotation. In view of the moderate rate of propeller rotation, only a moderate degree of flare of diffuser portion 14 results.

When the engine 2 is operating to rotate the propeller 8 at a high revolutions per minute and boat speed is relatively slow (as for example during acceleration), the centrifugal force is commensurately high and ram pressure relatively low. Under such conditions a high degree of flare of diffuser portion 14 results to good advantage to better accommodate the generally larger volume ofexhaust products.

When the propeller revolutions per minute and the boat speed are both high, the slipstream ram pressure overcomes most of the centrifugal force so that the resulting flare of diffuser portion 14 will be moderate. The moderate flare experienced during high speed operation is sufficiently; great to provide an adequate outward radial component to the water flowing over the propeller hub 12 to thus retard the water con vergence aft of the hub exhaust discharge opening 13, yet is sufficiently small to keep the underwater drag imposed by the flare near minimum.

According to the embodiment of H6. 4, an annular coil spring 24 is disposed in the annular radial enlargement 21 of diffuser portion 14 and serves as the flyweight for the diffuser portion in place of the eircumferentially spaced balls 22. Spring 24 must of course be heavy enough to overcome its own tension plus that of the resilient material of the diffuser portion 14 to be effective as a flyweight.

Iclaim:

1. In a propeller for a marine propulsion unit driven by an internal combustion engine, said propeller having radially spaced annular inner and outer hub elements to provide an annular passage therebetween for receiving and conducting engine exhaust products through the propeller hub for discharge rearwardly thereof, an annular radially expandable element secured on the rear end of the outer hub element and forming an extension thereof and providing an exhaust discharge opening for the propeller, said element being expandable radially adjacent to the exhaust discharge opening in response to contrifugal force resulting from propeller rotation in operation.

2. The invention as set forth .in claim 1 wherein flyweight means are provided in the expandable clement adjacent to the exhaust discharge opening.

3. The invention as set forth in claim 2 wherein the flyweight means comprise a plurality of circumferentially spaced ball weights.

4. The invention as set forth in claim 2 wherein the flyweight means comprise an annular spring means.

5. The invention as set forth in claim 2 wherein the terminal portion of the diffuser element adjacent to the exhaust discharge opening constitutes a radial enlargement and the flyweight means are molded into the enlargement.

6. The invention as set forth in claim 1 wherein the outer hub element of the propeller is stepped adjacent to the rear end thereof to provide an annular attachment flange extending rearwardly froma rearwardly facing shoulder and wherein the diffuser element is stepped adjacent to the forward end thereof to provide an annular attachment flange extending forwardly from a forwardly facing shoulder. said flanges on the outer hub element and diffuser element being complementary and bonded together with the respective flanges abutting the opposed shoulders to provide a generally smooth, uninterrupted transition between the elements both internally and externally.

7. The invention as set forth in claim 6 wherein the outer propeller hub element is stepped inwardly adjacent to the rear end thereof and the diffuser element is stepped outwardly adjacent to the forward end thereof to form the complementary attachment flanges. 

